(From CNN) It took just one day of use for several common sunscreen ingredients to enter the bloodstream at levels high enough to trigger a government safety investigation, according to a pilot study conducted by the Center for Drug Evaluation and Research, an arm of the US Food and Drug Administration.
The study, published Monday in the medical journal JAMA, also found that the blood concentration of three of the ingredients continued to rise as daily use continued and then remained in the body for at least 24 hours after sunscreen use ended.
The four chemicals studied -- avobenzone, oxybenzone, ecamsule, and octocrylene -- are part of a dozen that the FDA recently said needed to be researched by manufacturers before they could be considered "generally regarded as safe and effective."
In the United States, sunscreens were originally approved as an over-the-counter solution to sunburn. They came in two types: one using chemical combos to filter the sun, the other using minerals to block the sun such as titanium dioxide or zinc oxide, which leave a telltale white coating. With many people not wanting to sport a white tint, the popularity of the chemical sunscreens soared.
Because of the way they were used at the time, there wasn't a lot of concern about a potential health impact. But that soon changed, and the FDA began to ask the industry for safety testing, said David Andrews, senior scientist at the EWG.
"They were originally used in small quantities to prevent sunburn on vacation," Andrews said. "Now they recommend applying these every day, applying them to large parts of your body. And the FDA began raising concerns."
"The sun is the real enemy here," said Scott Faber, senior vice president for government affairs at the Environmental Working Group, or EWG, an advocacy group that publishes a yearly guide on sunscreens.
"Studies need to be performed to evaluate this finding and determine whether there are true medical implications to absorption of certain ingredients," said Yale School of Medicine dermatologist Dr. David Leffell, a spokesman for the American Academy of Dermatology. He added that in the meantime, people should "continue to be aggressive about sun protection."
Doctors say there are ways to protect yourself and your family other than sunscreen. Seek shade, especially between 10 a.m. and 2 p.m. when the sun is at its hottest, and whenever your shadow is shorter than you. Use protective clothing, such as long-sleeved shirts and pants and a hat with a wide brim, and don't forget the sunglasses.
"It's seeking shade, using clothes and when necessary using sunscreen," Andrews said, "but not using sunscreen to prolong your time in the sun."